1. Field of the Invention
The present invention relates to the field of coupler knuckles for use in coupling railroad cars and to methods for producing coupler knuckles.
2. Brief Description of the Related Art
Railroad vehicles are generally connected together with couplers. Railroad couplers are typically constructed to railroad standards so that couplers used on railroad cars may be coupled together, even if produced by different manufacturers. Common knuckles are American Association of Railroads (“AAR”) Standard E and F type railroad car couplers, and, in particular, the knuckles used in these couplers.
Railcar couplers are disposed at each end of a railway car to enable joining one end of such railway car to an adjacently disposed end of another railway car. The engageable portions of each of these couplers are known in the railway art as a knuckle. For example, railway freight car coupler knuckles are disclosed in numerous U.S. patents, such as, for example, including in the following U.S. patent documents: U.S. Pat. Nos. 461,312; 533,985; 693,998; 2,689,051; 2,088,135; 4,024,958; 4,206,849; 4,605,133; 5,582,307; 8,297,455 and U.S. patent application no. 2009/0289024. In addition, lightweight railway freight car coupler knuckles are disclosed in U.S. Pat. Nos. 5,954,212 and 6,129,227.
Coupler knuckles are generally manufactured from cast steel weighing approximately 84 lbs. The cast steel used is grade E, tensile strength 120,000 psi, yield strength of 100,000 psi, elongation of 14%, reduction of area 30%. These knuckles fatigue crack over time, which eventually leads to knuckle failure.
Knuckle failure accounts for about 100,000 train separations a year, or about 275 separations per day. Most of these separations occur when the train is out of a maintenance area. In such cases, a replacement knuckle, which can weigh about 80 pounds, must be carried from the locomotive at least some of the length of the train, which may be up to 25, 50 or even 100 railroad cars in length. The repair of a failed coupler knuckle can be labor intensive, can sometimes take place in very inclement weather, can cause train delays and, due to its excessive weight, subjects the carrier or carriers to potential lifting related injuries.
The front core of a knuckle is commonly referred to as the finger core. The finger core is commonly constructed to produce an internal cavity having thin ribs. These ribs made out of the standard grade E cast steel have demonstrated a weakness to the load environment with the development of fatigue and/or hot tear cracks. The fatigue cracks can grow over time and eventually lead to knuckle failure which results in separation of railcars. Separately, internal or external cracks in the knuckle are a cause for replacement of the knuckle. The rear core of a knuckle is commonly referred to as the kidney core. Knuckles can sometimes break within this portion of the knuckle and this has proven to be a very undesirable location for a failure. A failure in this region of the knuckle can lead to knuckle jamming within the coupler body and prevent a change out of a failed knuckle, thereby requiring the entire coupler assembly to be replaced, a very costly repair.
The core of the finished knuckle is generally seen as a cavity in the knuckle. However, it is the practice of a knuckle that is cast to cast the knuckle around a core. The common practice is to utilize a core within the casting, and then break the core apart when the knuckle has been cast. This practice, aside from being time consuming, generally requires precise positioning of the core, such as, in a jig, and that the core remain in position during the casting process. The current methods used for forming knuckles have drawbacks and are known to produce failures in the final product when the core is misaligned or has shifted during the forming process. In some instances, the metal itself that is used for the casting may shift the core when it contacts it, leading to an unusable part. U.S. Pat. No. 2,088,135 discloses a car coupler or coupler knuckle that is made from a casting.
U.S. Pat. No. 8,297,455 discloses the use of investment casting as a way to attempt to alleviate the problems of utilizing cores and the potential for core shifting, and to avoid the parting line between mold sections. The '455 patent discloses an investment casting method in which a prototype of a knuckle is formed, the prototype is coated with a slurry forming a shell, and then the prototype is removed from the shell. The '455 patent discloses using wax as the prototype and that the wax is melted and removed from the shell leaving a cavity. The component is then cast in the shell.
There is a need for a process for producing a knuckle that may be done with improved precision and less waste, and for a knuckle having improved capabilities for handling forces and having improved strength or fatigue life.
In addition, there is a need for a lightweight knuckle that is lower in weight than conventional knuckles and with strength or fatigue life similar to or exceeding those of heavier knuckles, where the lightweight knuckle operates to be the weak link in the coupler system and fail under high loading conditions.